The present invention relates to conformal-coated circuit packages and, in particular, to a method for forming and retrofitting a package to be compatible with pick and place handling equipment.
Varieties of discrete circuit devices are constructed with conformal coatings that physically and electrically protect the device from environmental conditions. That is, the coatings electrically insulate and protect the circuitry from moisture and physical damage. Separate conformal coatings may also be applied to higher-level circuit board assemblies containing the discrete parts.
A variety of conventional epoxy-based coating materials are known. The coatings can be applied using a variety of conventional techniques, for example, brush, roller, dip, spray, slit-die, among others. The coatings are cured using a variety of techniques, for example, ultraviolet curing (UV) or room temperature vulcanizing (RTV), among others compatible with the particular material, to provide a protective encapsulate.
Conformal coating processes, however, do not provide sufficient dimensional stability to accommodate conventional circuit handling equipment and circuit populating techniques. That is, surface imperfections and dimensional variations require hand mounting such devices.
In contrast, most integrated circuits are sealed in molded packages. The packaging is injection molded to relatively exact dimensions and tolerances. The result is that any contained electrical device can be adapted to conventional pick-and-place handling equipment. Such equipment is programmed to grip individual packages with suction or finger-type tool heads.
The subject invention was developed to provide alternative methods to make conformal-coated circuit devices that are compatible with standard circuit packaging equipment. One method provides conformal-coated devices that are mounted in injection-molded shells. Another method provides conformal-coated devices that include initially molded or re-formed surface regions that are dimensionally stable and uniquely located to be compatible with pick-and-place equipment.
It is a primary object of the invention to provide conformal-coated devices that are constructed to be compatible with automated parts handling equipment.
It is a further object of the invention to provide a device having a re-shaped conformal coating that is compatible with automated pick-and-place (PP) handling equipment.
It is a further object of the invention to provide an injection-molded shell adapted to contain a conformal-coated device and to support the device to be compatible with parts carriers and associated automated handling and equipment.
It is a further object of the invention to provide a method for re-flowing and molding a conformal coating material at a device to define a surface region that can be indexed and gripped by automated handling equipment.
It is a further object of the invention to provide thin film, conformal-coated circuit devices having flat surface regions that are adaptable to vacuum tool heads and fingered tool heads.
The foregoing objects, advantages and distinctions are obtained in one form of the invention wherein an open-sided, injection-molded shell is mounted around a conformal-coated device. The shell provides a dimensionally stable container that is compatible with tape carriers and tool heads for packaging equipment that is indexed to select the devices from the tape and place the devices on a circuit board.
Another form of the invention provides a method for re-flowing the conformal coating, adding additional coating material and contacting the heated device with a surface or placing the heated device into a mold to form a uniquely located and re-shaped surface region. The re-shaped surface region is positioned and shaped to be complementary with PP tapes and handling equipment.
Still other objects, advantages and distinctions of the invention will become more apparent from the following description with respect to the appended drawings. To the extent alternative constructions, improvements or modifications have been considered they are described as appropriate. The improvements may also be provided in alternative combinations and arrangements. The description should therefore not be literally construed in limitation of the invention. Rather, the scope of the invention should be broadly interpreted within the scope of the further appended claims.